A) Field of the Invention
The present invention relates to a magnetoresistance effect device having a pinning layer made of antiferromagnetic material containing Ir and Mn, a magnetic lamination structural body and a manufacture method for a magnetic lamination structural body.
B) Description of the Related Art
An exchange coupling film having a lamination structure consisting of an antiferromagnetic film and a ferromagnetic film is used to fix a magnetization direction of a ferromagnetic film used in a reading device of a hard disk drive (HDD) or a magnetoresistance effect type random access memory (MRAM).
FIG. 12 is a partial perspective view of a HDD reading device and a magnetic recording medium. An xyz orthogonal coordinate system is defined, xy-plane being defined on the surface of a magnetic recording medium 103 and z-axis being perpendicular to the surface of a magnetic recording medium 103. It is assumed that the x-axis direction corresponds to a trailing direction and the y-axis direction corresponds to a track width direction. A pair of magnetic shielding layers 100 and 101 is disposed at a distance from each other in the x-axis direction. A magnetoresistance effect device 102 is disposed between the magnetic shielding layers. The magnetoresistance effect device 102 faces the magnetic recording medium 103 with a micro gap therebetween in the z-axis direction. For example, a tunneling magnetoresistance effect device (TMR device) or a spin valve film is used as the magnetoresistance effect device 102.
A TMR device has a lamination structure of, for example, an underlying layer, an antiferromagnetic pinning layer, a ferromagnetic reference layer, a tunneling barrier layer, a free layer, and a cap layer stacked in the x-axis direction. A magnetic field generated from the magnetic recording medium 103 is sensed by the free layer of the magnetoresistance effect device 102, and a change in the magnetic field is read as an electric signal.
The pair of magnetic shielding layers 100 and 101 has a role of absorbing a magnetic field from bits adjacent to a target bit to be read. A bit length Lb depends therefore upon a total thickness (read gap length) Lrg of the magnetoresistance effect device 102. As the read gap length Lrg becomes long, the bit length Lb becomes long. It is desired to shorten the read gap length Lrg in order to shorten the bit length Lb.
Until the year of 2003, a Ta/NiFe laminated layer, a Ta/Ru laminated layer, a NiCr layer or a NiFeCr layer has been used as the underlying layer of a reading device for a HDD, and a PtMn layer or a PdPtMn layer has been used as the antiferromagnetic pinning layer. However, the antiferromagnetic pinning layer is required to have a thickness of 15 nm or thicker, in order for the antiferromagnetic pinning layer to be exchange-coupled with the ferromagnetic reference layer. As the pinning layer becomes thick, the read gap length Lrg becomes long. It is therefore difficult to improve a recording density by shortening the bit length Lb.
If IrMn is used for the pinning layer, the pinning layer is exchange-coupled with the pinned layer even if the pinning layer is thinned to about 4 nm. A magnetoresistance effect device using IrMn for the pinning layer is therefore suitable for improving a recording density (for example, refer to JP-A-2005-244254).
In order to exhibit the performance of a TMR device using MgO for the tunneling barrier layer at the maximum, it is preferable to make MgO have a (2 0 0) orientation. MgO can be made to have the (2 0 0) orientation by using amorphous CoFeB for the reference layer serving as the underlying layer of the tunneling barrier layer (refer to David D. Djayaprawira et al., “230% room-temperature magnetoresistance in CoFeB/MgO/CoFeB magnetic tunnel junctions”. Appl. Phys. Lett., 86, 092502 (2005)).
If IrMn is used for the pinning layer of a TMR device, a surface flatness of the pinning layer is degraded (surface roughness is increased). If the tunneling barrier layer is made thin to lower an area resistance RA of the TMR device, magnetostatic interaction between the reference layer and magnetization free layer becomes large because of surface irregularity of the reference layer. Therefore, a magnetization direction of the magnetization free layer is affected by magnetization of the reference layer. If the tunneling barrier layer of MgO is thin, pin holes are generated in the tunneling barrier layer because of surface irregularity of the reference layer, and the device performance may be degraded.
When the reference layer as the underlying layer of the tunneling barrier layer of MgO is made of amorphous CoFeB, MgO having a good (2 0 0) orientation can be obtained if the MgO film is grown to some thickness. However, if the MgO film is thin, it is difficult to form a film having a sufficient (2 0 0) orientation. As the orientation of the MgO film is degraded, an MR ratio lowers.